My first thought (from a sysadmin view, and only reading the title ;) ) is - firstboot scripts that only run once? The question sounds like they're looking for something a little more malicious I guess?...
Actually, bootscripts would probably count. The authors here mean code that can only run once and will unconditionally fail if it is executed more than once (such as #!/bin/rm), but a few of the examples can only be run once per session, which bootscripts would likely fit in.
